The cold truth about your fridge: So what temperature should it be, and which shelves are best for what foods? Your ultimate guide to getting the best out of your fridge

Mouldy vegetables, week-old ham or a plate of leftovers from Sunday lunch … Chances are that most of what you’ll find in the recesses of your fridge will end up in the bin.

According to a study by supermarket chain Sainsbury’s, British households throw away seven million tonnes of food waste every year — the equivalent of six meals a week.

And the surprising reason is that 75 per cent of us are running our fridges too warm. Just turning down the temperature could prevent up to 4.2 million tonnes of food waste a year and save each family a small fortune.

So what temperature should your fridge be, and which shelves are best for what foods?

Here SARAH RAINEY presents the ultimate guide …

HOW TO GET THE FRIDGE TEMPERATURE RIGHT

First things first: the temperature in your fridge isn’t constant. The fridge is cooled by a gas, known as refrigerant vapour, which flows in liquid form inside a coil in the fridge and absorbs heat in the air.

The closer foods are to the coil (which is usually found on the lower shelf, as hot air rises), the colder those foods will be.

Experts say the optimum overall temperature for a household fridge is between 0c and 4c.

Leading food safety expert Dr Lisa Ackerley says this is to prevent the growth of listeria — a harmful food poisoning bacterium that grows and spreads at temperatures above 5c.

‘Bacteria grow very slowly the lower the temperature,’ she adds.

‘Keeping your fridge below four degrees centigrade — but not below zero, the freezing temperature of water, which will turn the water in foods to ice — will ensure that it stays fresh for longer.’

A TOO-FULL FRIDGE COULD SPOIL YOUR FOOD

The more stuffed your fridge shelves become, the harder it is to keep cool. Just like a crowded room, a full fridge will be naturally warmer than an empty one. Experts recommend turning down the thermostat by one degree if you’ve totally filled it.

Nor will an empty fridge be very efficient. To prevent the cooling mechanism from working too hard and the fridge getting too cold, it’s advisable to keep a couple of jugs of water in the fridge to fill up space. Or you can turn the temperature setting up a notch.

Ideally, a fridge should be around three-quarters full to allow cold air to circulate unhindered and prevent pockets of heat from forming.

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HOW WILL I KNOW IF IT’S TOO WARM?

Aside from food going off before its best-before date, there are several signs to alert you that your fridge is at the wrong temperature.

If you have a modern fridge with a built-in digital thermometer, it will tell you — and some, such as most Bosch models, are fitted with an alarm which sounds when the temperature goes above 4c or drops below 0c.

In an older fridge that’s too warm, you may see condensation forming on the inside walls. This shows that the air in the fridge is turning from gas to liquid, which may contaminate food on the lower shelves.

If it’s too cold, there may be clusters of ice visible at the back. This could also be caused by a faulty door allowing warm air from the outside into the fridge.

This tricks the refrigerant vapour into thinking that it’s warmer than it is, so it absorbs more heat than necessary, causing the temperature to drop and ice crystals to form.

WHY DO SOME FOODS START TO FREEZE?

Though most of us have never bothered to look, almost all supermarket foods have a recommended storage temperature written on their packaging (normally between 3c and 5c).

Some foods — such as hard cheeses (which can be stored up to 10c) and bagged salad (which is fine up to 5c or 6c) — survive better at slightly higher temperatures, so being in a super-cold fridge can cause them to partially freeze.

This isn’t harmful to our health, says Dr Ackerley, but it may affect the taste of the foodstuffs.

Lettuce is mostly made of water, so the cell structure is destroyed when it freezes

‘Frozen cheese won’t harm you — just move it to another part of the fridge,’ she says.

‘As for salad, it will not be nice to eat if it goes soggy. Lettuce is mostly made of water, so the cell structure is destroyed when it freezes.’

If your fridge is fitted with a ‘crisper drawer’, store lettuce here instead. It seals in water vapour at around 2c, which keeps greens moist and crisp.

DO I NEED TO BUY A THERMOMETER?

Experts recommend buying a separate digital thermometer, even if you have a high-tech modern fridge. They say it’s the only guaranteed way of ensuring a constant temperature.

‘It’s best to use a thermometer,’ says Dr Ackerley. ‘Some fridges have an air cool system that distributes the temperature evenly, but in most fridges the lower parts may be cooler and the top door shelves warmer.’

Most supermarkets and hardware stores sell battery-operated thermometers that can be affixed to the inside of the door by a magnet or hooked onto a shelf. Tesco’s Hanson H2221 fridge thermometer costs £11.60, Maplin’s is £4.99, or an equivalent at Wilko costs £2.

AND WHAT IF IT’S HOT OUTSIDE?

Those hot summer days can affect the temperature of your fridge, just as they change the temperature of your home.

A recent study by the American Society of Heating, Refrigerating and Air Conditioning Engineers found that even when the fridge door is closed, changes in outside temperature can cause changes to the inside temperature of the fridge.

Dr Ackerley says these are minimal, though. ‘The fridge should be well enough insulated for it not to matter what the temperature is outside. But if it’s very hot, try to avoid leaving the fridge door open as this will allow cold air out and warm it up.’

If you are concerned your fridge is getting too hot or too cold, adjust the temperature — but no more than one degree either way, and never outside the 0-4c range.

WHAT CAN’T YOU PUT IN THE FRIDGE?

Compared with three or four decades ago, we’re compulsive fridge-users. However, plenty of everyday foods don’t actually need to be kept cold.

Professor Paul Berryman, a food science expert and visiting professor at the University of Reading, says some of these are taste-related, while other foods can undergo harmful reactions at lower temperatures.

‘Bananas, for example, go black in the fridge,’ he explains. ‘The cold temperature makes the plant cell vacuoles leak. The liquid contains phenolic compounds which react with an enzyme to form a brown substance called melanin.

Compared with three or four decades ago, we’re compulsive fridge-users. However, plenty of everyday foods don’t actually need to be kept cold like bananas

‘The same is true of bread. The cool temperature of a fridge makes it go stale faster, due to the effects on the starch.’

Other foodstuffs that should be kept out of the fridge are soft fruit such as peaches and plums (they need to be allowed to ripen), bitter (which tastes better unchilled) and potatoes.

The starch in potatoes is converted to sugar at a low temperature, and when baked or fried, the sugar reacts to form a harmful chemical called acrylamide.

CAN I USE IT TO STORE LEFTOVERS?

There’s no problem keeping leftovers in the fridge, as long as they’re well sealed (Tupperware containers are best) and cooled to room temperature first.

‘Cooling quickly is the key control to make sure it’s safe,’ says Dr Ackerley. ‘Decant leftovers into small portions and cool to room temperature in no more than two hours, then put them in the fridge. To speed cooling, put containers of food on ice and refresh pasta or rice with cold water.’

The fast cooling process prevents the growth of bacteria in leftovers.

Take particular care with cooked rice. Bacillus cereus — a bacterium that accounts for 5 per cent of all UK food poisoning — starts to produce toxic spores as soon as the rice cools. Chilling it properly slows down bacterial growth.

WHAT ABOUT OPEN JARS AND TINS?

Though it’s fine to keep a half-eaten portion of baked beans in the fridge, don’t store them in the tin.

Not only can the metal give the food an unpleasant taste, but chemicals used to treat the inside of the aluminium can react with what’s inside.

To stop toxins from contaminating the air of the fridge, ensure any open jars are tightly sealed.

Though it’s fine to keep a half-eaten portion of baked beans in the fridge, don’t store them in the tin

Experts recommend keeping condiments such as ketchup, mustard and jam in the fridge once open.

‘You should always follow the label,’ says Dr Ackerley.

‘Some products today have reduced sugar and salt, so they don’t preserve as well as they used to.’

HOW OFTEN SHOULD I CLEAN IT?

Dirt or spillages in your fridge can affect temperature by stopping cold air from moving freely.

Experts say you should clean your fridge thoroughly every month, using warm soapy water (not detergent) and a toothbrush to get into awkward corners.

You should also thaw your fridge, removing everything and switching it off at the mains, once a year. This helps regulate the temperature by removing any icy build-ups.

DO I NEED A LARDER AS WELL?

They’re the latest middle-class must-have, but from a food hygiene perspective, is a larder really necessary? Dr Ackerley says yes — but only for certain types of foods.

‘Larders are great for dried foods, flour, biscuits, vegetables and potatoes,’ she says. ‘But a fridge is the best place for perishable food because you can be sure of the temperature.’

As a cold, dark room, larders work well for foodstuffs that are chemically affected by sunlight (garlic, onions and herbs all go off more quickly when exposed to light). You can also use them for cheese, cured meats and tomatoes, whose taste is dulled by being chilled.

HOW TO ORGANISE YOUR FRIDGE

What you should keep in your fridge and where …

DRAWERS (2c): FRUIT AND VEG

As the only enclosed part of the fridge, the drawers are the most humid — perfect for fruit and veg, which thrive when there’s a bit of moisture in the air.

As fruit ripens, it releases ethylene, a gas that can make vegetables go rotten, so it’s best to keep fruit and veg in separate drawers

They’ll keep longest unwashed (water can promote mould and cause bacteria to grow) and in their original packaging or a plastic bag, which stops external toxins from puncturing the skin.

As fruit ripens, it releases ethylene, a gas that can make vegetables go rotten, so it’s best to keep fruit and veg in separate drawers.

BOTTOM SHELF (1c): RAW MEAT, FISH, POULTRY, DAIRY

This is the coldest part of the fridge, so milk will last longest here, pushed to the back where the temperature is the lowest.

Raw meat should also be kept on this shelf, because it’s coldest so will keep the meat fresh.

Raw meat should be kept on this shelf, because it’s coldest so will keep the meat fresh

But because the position in the fridge will prevent cross-contamination of other foods, which could lead to salmonella poisoning.

‘Putting it on the bottom shelf means it doesn’t drip on other foods,’ explains Prof Berryman.

Experts recommend storing raw meat, fish or poultry on a plate or in a box to keep it entirely separate from other foodstuffs.

MIDDLE SHELVES (2-3c): EGGS, DELI PRODUCTS

The central part of the fridge is where the temperature remains most constant, away from the extremes of the cooling coil and the door.

Raw eggs, whose fragile yolks are affected by changes in temperature, are best kept here.

Raw eggs, whose fragile yolks are affected by changes in temperature, are best kept in the middle shelves

Eggs also work to absorb odours from the air, so keeping them in a central position will help remove unsavoury smells.

Cured meats, olives and other deli products should be kept here, too.

They don’t need to be kept super-cold, so light refrigeration will do.

TOP SHELF (3c): WINE, LEFTOVERS

The optimum temperature for storing wine is 5-7c, so a fridge is technically a little too cold for most bottles.

But if you do like yours extra-chilled, stick it on the top shelf, where it’s a balmy 3c.

This is better than storing it in the door, as wine is meant to be kept on its side, not upright.

If you do like yours extra-chilled, stick it on the top shelf of the fridge, where it’s a balmy 3c

This stops oxygen from seeping in and spoiling the liquid.

Up at the top, it’s also furthest from the cooling coil, whose vibrations can affect the delicate balance of the wine.

This is a good place, too, to keep other foods that don’t need excessive chilling: leftovers, nuts (which keep for longer in the fridge) and preservative-heavy ready meals.